1. Field of the Invention
The present invention relates to a Flexible Printed Circuit for mounting components (hereinafter referred to as FPC) with an improved workability of fitting into other components, and to a spread illuminating apparatus using the FPC.
2. Description of the Related Art
Recent electric products have been provided with a function to display various information, so that it has become indispensable for those products to have a display portion to display the information. In case of portable electronic products such as portable telephones and notebook computers, in which all components are desired to be reduced in dimension and weight, a liquid crystal display device (the ratio of the thickness to the display area is extremely small), which occupies a small volume in the product and is lightweight, is generally used for the display portion. However, since the liquid crystal display device does not emit light by itself, it will be necessary to provide a separate illuminating apparatus besides the liquid crystal display device when used in dark places or at night. Based on the above demand, a spread illuminating apparatus described hereinafter is designed to achieve a uniform illumination over the entire display portion.
The spread illuminating apparatus illuminates entirely the liquid crystal display device in such a way that when the transparent substrate is illuminated at its end surface, light rays are directed into a transparent substrate made of a light-transmissible material and provided on the front or back surface of the liquid crystal display device and are uniformly supplied from the surface of the transparent substrate toward the display portion of the liquid crystal display device.
A fluorescent tube (cold cathode fluorescent tube or hot cathode fluorescent tube) has been conventionally used as a light source for illuminating the end surface of the transparent substrate. However, since the fluorescent tube requires a high voltage to emit light, a means for supplying a high voltage is necessary. This conflicts with the miniaturization required for the components of portable products.
In order to solve the above problems, the inventors of the present invention have developed a spread illuminating apparatus using a spot-like light source such as light emitting diodes, and disclosed in detail in the Japanese Patent Application No. Hei 10-182076. This spread illuminating apparatus using a light emitting diode as a light source is briefly explained below with reference to FIGS. 5 to 8.
In FIGS. 5 to 7, this spread illuminating apparatus 1 is generally composed of a transparent substrate 2 made of a light-transmissible material, and a bar-like light source 4 disposed close to an end surface 3 of the transparent substrate 2. A liquid crystal panel 5 is provided at the lower surface of the transparent substrate 2 and this spread illuminating apparatus 1 is to be used as a subsidiary illumination for the liquid crystal panel 5. Further, a box-shaped metallic frame 6 is provided so as to cover the spread illuminating apparatus 1 and the liquid crystal panel 5.
The transparent substrate 2 is formed in a wedge-shape, that is, the thickness of the transparent substrate 2 is in inverse proportion to the increase in distance from the end surface 3 and gradually decreases.
The light source 4 is generally composed of a light conductive member 7 (FIG. 7) made of a transmissible material, formed in a triangular long-plate shape and disposed close to and along the end surface 3 of the transparent substrate 2, and a spot-like light source 8 disposed facing one end 7a of the light conductive member 7 and mounted on an FPC 9.
A surface 7c (second surface of light conductive member) of the light conductive member 7 opposing a surface 7b (first surface of light conductive member) facing the transparent substrate 2 is slanted with respect to the first surface 7b of the light conductive member in a plan view. The second surface 7c of the light conductive member is provided with an optical path conversion means 10 which is composed of grooves 10a substantially triangular in section and flat portions 10b each formed between two adjacent grooves 10a. Therefore, light rays which enter the one end 7a of the light conductive member 7 can be uniformly emitted at the first surface 7b of the light conductive member despite the spot-like light source 8 being disposed at the one end 7a. 
A light reflection pattern 12 is formed on a surface 11 of the transparent substrate 2 (the upper side in FIG. 7, hereinafter referred to as upper surface). Thus, the brightness is almost uniform everywhere on the transparent substrate 2 irrespective of the distance from the light conductive member 7.
A light emitting diode prepared as a chip component and functioning as the spot-like light source 8 is mounted on the FPC 9, and a terminal 14 thereof is connected to a copper foil 15 (conductive member) by soldering. A solder fillet 16 is shown with hatching in FIG. 6.
In the conventional art shown in FIGS. 5 to 7, the terminal 14 and the solder fillet 16 are disposed close to the metallic frame 6, where a short circuit may occur. And, while it is desired for light rays emitted from the spot-like light source 8 to enter the light conductive member 7 efficiently, the spot-like light source 8 is provided in such a manner as to be substantially exposed. As a result, light rays L leak outward from the periphery of the spot-like light source 8 as shown in FIG. 8, decreasing the efficiency of light incidence. The present inventors have disclosed means for solving the above problems in detail in Japanese Patent Application No. Hei 11-375192 or the other related application, and the means are structured as shown in FIG. 9.
The FPC 9 is generally composed of a rectangular portion (substrate) 19 on which the spot-like light source 8 is mounted, and a cover portion 20 extending from the substrate 19 and encasing the spot-like light source 8 for electrically insulating from its periphery. The cover portion 20 has a rectangular face portion (first face portion) 22 which is orthogonal to and continuous with the substrate 19 and bent (this bent portion is referred to as first bend 21) along the wall surface of the spot-like light source 8. A rectangular face portion 24 (second face portion) is formed in such a manner as to be orthogonal to and continuous with the first face portion 22, to be bent (this bent portion is referred to as second bend 23) along the wall surface of the spot-like light source and to be in parallel with the substrate 19. Further, a rectangular face portion (third face portion) 26 is formed in such a manner as to be orthogonal to the bend 23, to extend from the first face portion 22 and to be bent (this bent portion is referred to as third bend 25) along the wall surface of the spot-like light source.
A space 27 defined by the substrate 19, the first, second and third face portions 22, 24 and 26 accommodates the spot-like light source 8 mounted on the substrate 19. The space 27 has non-definition (referred to as first opening 28) at the side opposing the first face portion 22. The spot-like light source 8 and the FPC 9 are disposed in such a manner that this first opening 28 faces the end 7a of the light conductive member 7 so as to make light rays from the spot-like light source 8 enter the light conductive member 7. The portions denoted by reference numeral 15 in FIG. 9 are metallic foil (copper foil) provided on the FPC 9. The copper foil(s) 15 extends from the substrate 19 to the first face portion 22, and the copper foil(s) 15 at the first face portion 22 is connected to the spot-like light source 8.
In the above structure, the cover portion 20 (substrate 19, the first, second and third face portions 22, 24, 26) ensures that the spot-like light source 8 is insulated from the metallic frame 6 while preventing the light rays from leaking outward from the periphery of the spot-like light source 8, thereby solving the above problems. However, the cover portion 20 raises a new problem when the FPC 9 and the spot-like light source 8 are set in the metallic frame 6.
The new problem is that the first bend 21, the second bend 23 and the third bend 25 do not bend as desired and rebound by elastic recovery generated due to the properties of raw materials of the FPC 9 (polyimide, polyester and the like). Because of this inconvenience and the small size as well, the workability of setting the FPC 9 into the metallic frame 6 is remarkably lowered. Moreover, the FPC 9 itself may crack when a strong force is applied to force each bend to retain its shape. Further, even after assembly, the cover portion 20 expands with time within the metallic frame 6 and may shift off a predetermined position. Note that, the above problem is not limited to the specific FPCs used in spread illuminating apparatuses, but it is applicable to all FPCs that are bent along the wall surface of chip components mounted thereon.
The present invention has been made in the light of the above problems, and the object of the present invention is to prevent each bend from rebounding due to elastic recovery, thereby improving workability of setting an FPC for mounting components into other components. Further, another object of the present invention is to improve the workability of setting in while ensuring insulation of a light emitting diode prepared as a chip component and functioning as spot-like light source and preventing light rays from leaking outward from the periphery of the spot-like light source when the FPC for mounting components is used in a spread illuminating apparatus.
In order to solve the above problems, according to a first aspect of the present invention, there is provided an FPC for mounting components, which is bent along a wall surface of a mounted chip component, characterized in that a core material which can be plastically transformed is provided at a bend. According to the present invention, the core material prevents the bend from rebounding due to the elastic recovery of the FPC for mounting components, thereby enabling the bend to retain its shape as desired.
Further, according to a second aspect of the present invention, in the FPC for mounting components according to the first aspect of the present invention, a plurality of bends are provided and the core material is disposed at all of the bends. According to this structure, a plurality of wall surfaces of the chip components can be covered with the FPC. And, the core material is disposed at each of the bends, which prevents each bend from rebounding, thereby enabling the bend to retain its shape as desired.
According to a third aspect of the present invention, in the FPC for mounting components according to second aspect of the present invention, the core material is a metallic foil constituting an FPC pattern. Therefore, the core material can be formed simultaneously with the pattern for mounting the chip components.
Further, according to a fourth aspect of the present invention, in the FPC for mounting components according to the third aspect of the present invention, the difference in area between the patterns continuous with pads of both electrodes, on which terminals of the chip components are mounted, is reduced as needed. With this structure, the difference in heat capacity between the pads of both electrodes is reduced, and a problem (chip standing) during re-flow soldering can be prevented.
Further, according to a fifth aspect of the present invention, there is provided a spread illuminating apparatus, in which a bar-like light source comprising a light conductive member made of a transmissible material, formed bar-like and disposed close to and along at least one end surface of a transparent substrate and a spot-like light source disposed on at least one end of the light conductive member and mounted on an FPC, is disposed close to the end surface of the transparent substrate made of a light-transmissible material, the spread illuminating apparatus being characterized by employing the FPC for mounting components according to any one of the first to fourth aspects of the present invention.
According to the present invention, the core material provided at the FPC enables the prevention of the rebound of the FPC due to the elastic recovery, and the bend can retain its shape as desired. Thus, the workability of setting the FPC into other components is improved.